Interested

The curriculum is in desperate need of clarification. I was very lost in this lesson and swear that you just taught us this IS correct and valid, yet you are now saying it is not. I went back to clarify my understanding and found this. In the lesson titled "other formal arguments" within the "Logic of intersecting sets" tab you cover something similar. To be noted what the curriculum states is that

A→B‑m→C leads to A←s→C

Which is NOT valid.

However.

A→B

A‑m→C leads to B←s→C which IS valid.

Apparently A to C is a stretch, but B to C is not a stretch and is actually valid with the some quantifier.

Can an instructor or someone confirm this is right?

I am interested!